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4. Intelligent power module
IPM consists of the following components
· IGBT (x6)
: Converts DC waveform to three-phase AC waveform and outputs it.
· Drive Circuit
: Drives transistors.
· Protection circuit
: Protects transistors from overcurrent.
Since the above components are all integrated in IPM, IPM has a merit to make the control circuit simplify and miniaturize.
5. Smoothing capacitor
C63A, C63B and C63C stabilize the DC voltage and supply it to IPM.
6. Elimination of electrical noice
Noise filter circuit, which is formed by *CMC COILS capacitors placed on the POWER P.C. board, eliminates electrical
noise of AC power that is supplied to main power supply circuit. And this circuit prevents the electrical noise generated in
the inverter circuit from leaking out.
*CMC COILS; Common mode choke coils
Outline of simple partial switching method
In conventional inverter models, diode module rectifies AC voltage to DC voltage, smoothing capacitor makes its DC waveform
smooth, and IPM converts its DC voltage to imitated AC voltage again in order to drive the compressor motor.
However, it has been difficult to meet IEC harmonic current emission standard by above circuit because harmonic gets
generated in the input current waveform and power factor gets down. The simple partial switching method with PAM, which has
been adopted this time, places and utilizes the booster chopper circuit (L64, DB65 and TR821) before rectifying AC voltage in
the general passive-method converter circuit. As harmonic gets suppressed and the peak of waveform gets lower by adding
booster chopper circuit as mentioned above and by synchronizing the timing of switching with the zero-cross point of
waveform, the input current waveform can be improved and the requirement of IEC harmonic current emission standard can be
satisfied. Since the switching is synchronizied with the zero cross point, this simple partial switching method has
the feature of lower energy loss compared to active filter method. In addition, output and efficiency is enhanced by
combining with vector-controlled inverter in order to boost the voltage of power supplied to IPM.
Input current waveform without PAM
Due to the time of no electricity;
· Power factor gets worse.
· Harmonic gets increased.
Input voltage
Energized time is short in
case L inductance is small.
No electricity runs into
diode module because the
voltage at both sides of smoothing
capacitor is higher than input voltage.
Input current
Input current waveform with PAM
Owing to the increase of energized time;
· Power factor gets better.
· Harmonic gets suppressed.
Energized time is
extended by optimization
of L inductance.
Peak gets down.
Release of energy stored in L
Compulsory energizing
by switching.
12-1-2. Outline of main power supply circuit
MXZ-2A30/40/52VA
1. At the start of operation
Main power supply circuit is formed when X64 (Relay) is turned ON at compressor startup.
To prevent rush current from running into the circuit when power supply is turned ON,
R64A and R64B (Current-limitting resistor) are placed in sub circuit.
2. At normal operation
1
When AC runs into POWER P.C. board, its external noise is eliminated in the noise filter circuit.
2
After noise is eliminated from AC, it is rectified to DC by DB61 (Diode module).
3
DC voltage, to which AC has been rectified by process
2
, is stabilized by C63A, C63B and C63C (Smoothing capacitor)
and supplied to IPM (Intelligent power module).
4
DC voltage, which has been stabilized in process
3
, is converted to three-phase AC by IPM and supplied to
compressor.
5
CT761 and CT781 (Current Transformer), which are placed in the power supply circuit to compressor, are used to
measure the value of phase current and locate the polar direction of rotor with algorithm. PWM (Pulse width modulation)
controls impressed voltage and frequency with those information.
3. Purpose of PAM adoption
PAM : Pulse Amplitude Modulation
PAM has been adopted for the efficiency improvement and the adaptation to IEC harmonic current emission standard.
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